Diffraction-Based Overlay Metrology for Lithography
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Solution Overview
Problem
Current methods for determining parameters in pattern transfer processes, such as lithography, face challenges in accurately measuring errors like overlay and critical dimension, which can lead to functional issues in devices due to imaging errors and other process inaccuracies.
Innovation Solution
A method involving the detection of radiation redirected by a structure formed through pattern processing, where a unit cell is mirror symmetric, to determine asymmetry and thereby assess parameters of the pattern transfer process, allowing for adjustments to improve process accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional metrology methods are used to measure overlay and critical dimension, then measurement can be performed, but measurement precision is insufficient due to imaging errors and process inaccuracies
Solution Approach 1:
The patent applies asymmetry by using asymmetric illumination to deliberately create asymmetric diffraction patterns from symmetric structures. When overlay error is present, the diffraction intensities from opposite sides become unequal, allowing precise measurement of the overlay parameter. This converts the measurement problem into detecting asymmetry in the diffraction pattern, achieving high measurement precision while maintaining reliability.
2Manufacturing precision
If imaging errors and process inaccuracies are present in pattern transfer, then device manufacturing can proceed, but manufacturing precision deteriorates due to overlay and critical dimension errors
Solution Approach 1:
The patent implements feedback by measuring overlay and critical dimension parameters using diffraction-based metrology and using these measurements to control and adjust the pattern transfer process. The measured parameters provide feedback information that allows real-time correction of process deviations, maintaining manufacturing precision and ensuring device functionality despite inherent process variations.
3Measurement precision
If diffraction-based metrology with asymmetric illumination is used, then measurement precision improves for overlay and critical dimension, but device complexity increases due to additional measurement apparatus and processing
Solution Approach 1:
The patent applies universality by designing a metrology target and illumination system that can measure multiple parameters (overlay and critical dimension) simultaneously using the same apparatus. The asymmetric illumination setup and diffraction-based measurement method provide a multi-functional solution that improves measurement precision for both parameters without requiring separate dedicated measurement devices for each parameter.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise measurement of asymmetries in pattern transfer processes, enabling better control and reduction of errors, thus enhancing the accuracy and reliability of device manufacturing.
Implementation Method 1
Illuminating the structure with radiation and obtaining a detected representation of radiation redirected by the structure
Implementation Method 2
obtaining a detected representation of radiation redirected by the structure
Data Source
AI summary
A method of determining a parameter of a pattern transfer process and device manufacturing methods are disclosed. In one arrangement, a method includes obtaining a detected representation of radiation redirected by a structure. The structure is a structure formed by applying a pattern processing to a pattern transferred to an earlier formed structure by a pattern transfer process. The pattern processing is such as to remove one or more selected regions in a horizontal plane of the earlier formed structure to form a pattern in the horizontal plane. The pattern is defined by a unit cell that is mirror symmetric with respect to an axis of mirror symmetry. An asymmetry in the detected representation is determined. The determined asymmetry in the detected representation is used to determine a parameter of the pattern transfer process.